Original Research Article
Elements characterization of Chinese tea with different fermentation degrees and its use for geographical origins by liner discriminant analysis

https://doi.org/10.1016/j.jfca.2019.103246Get rights and content

Highlights

  • 33 elements of Chinese teas were determined by ICP-MS.

  • The elements levels varied with different tea types.

  • High recognition and satisfactory predictive ability were achieved by LDA.

Abstract

Elements profiling of teas are very important not only for quality control of tea, but also providing comprehensive database for risk assessment of human health. 33 elements in 313 tea samples collecting from representative provinces of China were analyzed. The levels of elements varied with different tea types. Puerh tea had the highest mean concentrations of Al (862 ± 405 mg kg−1), Cr (2.51 ± 1.6 mg kg−1), As (0.14 ± 0.10 mg kg−1), Mg (2313 ± 830 mg kg−1), Cs (0.56 ± 0.63 mg kg−1) and REEs (1.33 ± 1.0 mg kg−1) and lowest mean levels of Co (0.22 ± 0.11 mg kg−1), Ni (6.27 ± 3.4 mg kg−1), Zn (33.8 ± 11 mg kg−1) and Pb (0.81 ± 0.74 mg kg−1) compared to green teas and black teas. However, the highest mean levels of Ni (14.5 ± 13 mg kg−1), Cu (24.6 ± 12 mg kg−1), Zn (52.7 ± 18 mg kg−1), Mo (0.28 ± 0.14 mg kg−1) and Pb (1.16 ± 0.86 mg kg−1) were found in black teas. Green teas were measured with lowest contents of elements among three types of teas. High recognition (98.4%) and satisfactory predictive ability (97.8%) were achieved for three types of tea with different fermentation degrees by liner discriminant analysis. Moreover, black teas from five different regions could be easily distinguished with each other based on the elements with significant differences.

Introduction

The contents of elements in plants were affected not only by the geochemical characteristics of the soil but also the ability of plant species to selectively accumulate certain elements (Cindric et al., 2015). Tea, as one of the most popular nonalcoholic beverage, had attracted the world's concern in the past thousands of years. It was produced from the leaves of Camellia sinensis, which was normally grown in the acidic soils, where trace elements were potentially more bioavailable for root uptake (Han et al., 2006; Seenivasan et al., 2016). Some elements including calcium, manganese, iron, copper, zinc, selenium etc. are considered essential, which is necessary for tea plant growth or physiological function and beneficial for human health (Phan-Thien et al., 2012; Reeves and Hoffmann, 2009). However, when present in sufficiently high concentrations, some essential elements can exhibit toxic effects. For example, accumulation of aluminium (Al) in tea infusion was associated with Alzheimer's disease (McLachlan, 1995; Rondeau et al., 2000). Besides Al, it was reported that rare earth elements (REEs) increased in environmental and biological samples and finally impaired human health by food chain (Hirano and Suzuki, 1996; Li et al., 2012). Moreover, heavy metals like cadmium (Cd), chromium (Cr), lead (Pb) and arsenic (As) are considered to be toxic metals. Prolonged consumption of heavy metals from food could lead to their accumulation in the kidney and liver, causing disruption of numerous biochemical processes and potentially causing cardiovascular, nervous, kidney and bone diseases(Lee and Thevenod, 2008; Sanchez-Chardi et al., 2009; Satarug, 2012). Thus, contents of elements in tea leaves remain a concern and good quality control is needed to ensure their safe use for consumers.

According to the processing procedures, tea can be classified into green tea (non-fermented), oolong tea (semi-fermented), black tea (fully fermented by oxidizing enzyme) and dark tea (post-fermented by microbe). Numerous efforts have been devoted to determine the mineral metal levels in tea (Moreda-Piñeiro et al., 2003; Abd El-Aty et al., 2014; Karak and Bhagat, 2010). Trace elements and REEs were determined in green tea from different geographical regions (Ma et al., 2016; Brzezicha-Cirocka et al., 2016a; Koch et al., 2018; Zhang et al., 2018a). Macro- and Microelement were monitored in black tea or CTC black tea (Brzezicha-Cirocka et al., 2017; Zhang et al., 2018b). The exposure of metals in puerh tea was determined to evaluate the possible health risk (Cao et al., 2010; Zhang et al., 2017; Brzezicha-Cirocka et al., 2016b). The REEs in oolong made tea and tea infusion were investigated to assess the risk of REEs to human health (Guo et al., 2015). Mineral elements contents were used to identify the origin of white tea in China (Ye et al., 2017). Although there were various researchers had been reported the contents of elements in different types of teas to classify the geographical origins separately, only a few studies focused on the comparative evaluation of multi-element for different types of teas. Five toxic elements were determined in different types of teas in China. It was found that As concentration of blank tea was higher compared to green tea, oolong tea, while green tea had the higher levels of Cd (Han et al., 2005). The contents of 12 elements were quantified in different types of teas (30 samples) from markets in southeastern Brazil (Milani et al., 2016). It has still limited detailed studies on the multi-element concentrations in different types of teas in China. In order to clarify and character the multi-element in Chinese tea samples with different fermentation degrees, large number of tea samples from different tea production regions of China should be collected.

Yunnan province (Southwest China) is an important and main area for puerh tea production of China (Fig. 1 blue area). Nowadays, puerh tea, one of the most representative dark tea, has been favored by more and more people, especially in China, Southeast Asia and France, owing to its health effect against cancer, decrease blood glucose, etc (Lv et al., 2013a). Two provinces of Zhejiang and Jiangsu are typical regions for green tea production. They have very famous historical green teas like Xihulongji (Wang et al., 2014; Ni et al., 2018) and Dongting Biluochun (Ma et al., 2016) (Fig. 1 green parts). Five representative provinces of black teas production including Henan, Hubei, Anhui, Fujian and Guangdong were chosen in our study (Fig. 1 red areas). Here, total 313 tea samples were collected from above eight provinces of China. 33 elements including toxic metal, essential elements, REEs etc. were analyzed for each tea samples. The present study had the following main aims: a) to profile the levels of main elements in tea samples of China, b) to investigate the variability of the contents of elements in different types of teas from different region, c) to classify the types and geographic origins of tea samples based on the elements with significant differences through multivariate analysis. Our study is very important not only for the quality control of teas, but also providing the comprehensive database for risk assessment of human health.

Section snippets

Chemicals

Nitric acid (Fisher Scientific, Shanghai, China), the multi-element atomic spectroscopy standard solution V (Sigma-aldrich Chemie GmbH, Buchs, Switzerland) were used for standard solution. For REEs, a series of calibration solutions with different concentrations of REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) were prepared using the standard solutions (National Analysis Center for Iron and Steel in Beijing, China). The content of each REE was converted into the content

Method validation

In order to evaluate the accuracy and reliability of the method, CRM of green tea (GBW10052) was analyzed. The sample analyses were made in triplicates and results were given in Table 1. It could be seen that the determined values were in good accordance with the certified value, indicating a good accuracy of the sample data generated. Recoveries of the studied elements ranged between 86.3 and 107.7% (RSDs<5%) of the certified values for all the elements. Limits of detection and quantification

Conclusions

In summary, 33 elements were measured in 313 tea samples with different fermentation degrees from eight provinces in China. The total concentrations of toxic metals, essential elements, REEs and other elements in all tea samples were discussed separately. The levels of elements varied with different tea types. Al, Cr, As, Mg, Cu and REEs showed the lowest average levels in green tea samples, while black teas were found with high mean concentrations of Cu, Zn, Ni, Mo, and Pb. The highest mean

Acknowledgements

We are grateful for financial support from Modern Agro-Industry Technology Research System (CARS-19) and the tea quality and risk assessment of innovation team of science and technology innovation project in Chinese Academy of Agricultural Sciences (CAAS-ASTIP-2017-TRICAAS).

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